refactor(tvix/store): use composition in tvix_store crate

Change-Id: Ie6290b296baba2b987f1a61c9bb4c78549ac11f1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11983
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: yuka <yuka@yuka.dev>
Tested-by: BuildkiteCI

tvix/castore/src/composition.rs

@@ -454,4 +454,11 @@ impl Composition {
         *entry = Box::new(new_val);
         ret
     }
+
+    pub fn context(&self) -> CompositionContext {
+        CompositionContext {
+            stack: vec![],
+            composition: Some(self),
+        }
+    }
 }

tvix/cli/src/lib.rs

@@ -60,7 +60,7 @@ pub fn init_io_handle(tokio_runtime: &tokio::runtime::Runtime, args: &Args) -> R
     Rc::new(TvixStoreIO::new(
         blob_service.clone(),
         directory_service.clone(),
-        path_info_service.into(),
+        path_info_service,
         nar_calculation_service.into(),
         build_service.into(),
         tokio_runtime.handle().clone(),

tvix/glue/benches/eval.rs

@@ -34,7 +34,7 @@ fn interpret(code: &str) {
     let tvix_store_io = Rc::new(TvixStoreIO::new(
         blob_service,
         directory_service,
-        path_info_service.into(),
+        path_info_service,
         nar_calculation_service.into(),
         Arc::<DummyBuildService>::default(),
         TOKIO_RUNTIME.handle().clone(),

tvix/glue/src/builtins/mod.rs

@@ -80,7 +80,7 @@ mod tests {
         let io = Rc::new(TvixStoreIO::new(
             blob_service,
             directory_service,
-            path_info_service.into(),
+            path_info_service,
             nar_calculation_service.into(),
             Arc::<DummyBuildService>::default(),
             runtime.handle().clone(),

tvix/glue/src/tests/mod.rs

@@ -41,7 +41,7 @@ fn eval_test(code_path: PathBuf, expect_success: bool) {
     let tvix_store_io = Rc::new(TvixStoreIO::new(
         blob_service,
         directory_service,
-        path_info_service.into(),
+        path_info_service,
         nar_calculation_service.into(),
         Arc::new(DummyBuildService::default()),
         tokio_runtime.handle().clone(),

tvix/glue/src/tvix_store_io.rs

@@ -648,7 +648,7 @@ mod tests {
         let io = Rc::new(TvixStoreIO::new(
             blob_service,
             directory_service,
-            path_info_service.into(),
+            path_info_service,
             nar_calculation_service.into(),
             Arc::<DummyBuildService>::default(),
             tokio_runtime.handle().clone(),

tvix/nar-bridge/src/bin/nar-bridge.rs

@@ -55,7 +55,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
         )
         .await?;
 
-    let state = AppState::new(blob_service, directory_service, path_info_service.into());
+    let state = AppState::new(blob_service, directory_service, path_info_service);
 
     let app = nar_bridge::gen_router(cli.priority).with_state(state);
 

tvix/store/src/bin/tvix-store.rs

@@ -16,7 +16,6 @@ use tracing::{info, info_span, instrument, Level, Span};
 use tracing_indicatif::span_ext::IndicatifSpanExt as _;
 use tvix_castore::import::fs::ingest_path;
 use tvix_store::nar::NarCalculationService;
-use tvix_store::pathinfoservice::CachePathInfoService;
 use tvix_store::proto::NarInfo;
 use tvix_store::proto::PathInfo;
 
@@ -210,31 +209,38 @@ async fn run_cli(cli: Cli) -> Result<(), Box<dyn std::error::Error + Send + Sync
             remote_path_info_service_addr,
         } => {
             // initialize stores
-            let (blob_service, directory_service, path_info_service, nar_calculation_service) =
-                tvix_store::utils::construct_services(
-                    blob_service_addr,
-                    directory_service_addr,
-                    path_info_service_addr,
-                )
-                .await?;
+            let mut configs = tvix_store::utils::addrs_to_configs(
+                blob_service_addr,
+                directory_service_addr,
+                path_info_service_addr,
+            )?;
 
             // if remote_path_info_service_addr has been specified,
             // update path_info_service to point to a cache combining the two.
-            let path_info_service = if let Some(addr) = remote_path_info_service_addr {
-                let remote_path_info_service = tvix_store::pathinfoservice::from_addr(
-                    &addr,
-                    blob_service.clone(),
-                    directory_service.clone(),
-                )
-                .await?;
+            if let Some(addr) = remote_path_info_service_addr {
+                use tvix_store::composition::{with_registry, DeserializeWithRegistry, REG};
+                use tvix_store::pathinfoservice::CachePathInfoServiceConfig;
 
-                let path_info_service =
-                    CachePathInfoService::new(path_info_service, remote_path_info_service);
+                let remote_url = url::Url::parse(&addr)?;
+                let remote_config = with_registry(&REG, || remote_url.try_into())?;
 
-                Box::new(path_info_service) as Box<dyn PathInfoService>
-            } else {
-                path_info_service
-            };
+                let local = configs.pathinfoservices.insert(
+                    "default".into(),
+                    DeserializeWithRegistry(Box::new(CachePathInfoServiceConfig {
+                        near: "local".into(),
+                        far: "remote".into(),
+                    })),
+                );
+                configs
+                    .pathinfoservices
+                    .insert("local".into(), local.unwrap());
+                configs
+                    .pathinfoservices
+                    .insert("remote".into(), remote_config);
+            }
+
+            let (blob_service, directory_service, path_info_service, nar_calculation_service) =
+                tvix_store::utils::construct_services_from_configs(configs).await?;
 
             let mut server = Server::builder().layer(
                 ServiceBuilder::new()
@@ -257,7 +263,7 @@ async fn run_cli(cli: Cli) -> Result<(), Box<dyn std::error::Error + Send + Sync
                     GRPCDirectoryServiceWrapper::new(directory_service),
                 ))
                 .add_service(PathInfoServiceServer::new(GRPCPathInfoServiceWrapper::new(
-                    Arc::from(path_info_service),
+                    path_info_service,
                     nar_calculation_service,
                 )));
 
@@ -302,8 +308,7 @@ async fn run_cli(cli: Cli) -> Result<(), Box<dyn std::error::Error + Send + Sync
                 )
                 .await?;
 
-            // Arc PathInfoService and NarCalculationService, as we clone it .
-            let path_info_service: Arc<dyn PathInfoService> = path_info_service.into();
+            // Arc NarCalculationService, as we clone it .
             let nar_calculation_service: Arc<dyn NarCalculationService> =
                 nar_calculation_service.into();
 
@@ -365,9 +370,6 @@ async fn run_cli(cli: Cli) -> Result<(), Box<dyn std::error::Error + Send + Sync
             let reference_graph: ReferenceGraph<'_> =
                 serde_json::from_slice(reference_graph_json.as_slice())?;
 
-            // Arc the PathInfoService, as we clone it .
-            let path_info_service: Arc<dyn PathInfoService> = path_info_service.into();
-
             let lookups_span = info_span!(
                 "lookup pathinfos",
                 "indicatif.pb_show" = tracing::field::Empty
@@ -475,7 +477,7 @@ async fn run_cli(cli: Cli) -> Result<(), Box<dyn std::error::Error + Send + Sync
                 let fs = make_fs(
                     blob_service,
                     directory_service,
-                    Arc::from(path_info_service),
+                    path_info_service,
                     list_root,
                     show_xattr,
                 );
@@ -523,7 +525,7 @@ async fn run_cli(cli: Cli) -> Result<(), Box<dyn std::error::Error + Send + Sync
                 let fs = make_fs(
                     blob_service,
                     directory_service,
-                    Arc::from(path_info_service),
+                    path_info_service,
                     list_root,
                     show_xattr,
                 );

tvix/store/src/composition.rs

@@ -0,0 +1,22 @@
+use lazy_static::lazy_static;
+
+pub use tvix_castore::composition::*;
+
+lazy_static! {
+    /// The provided registry of tvix_store, which has all the builtin
+    /// tvix_castore (BlobStore/DirectoryStore) and tvix_store
+    /// (PathInfoService) implementations.
+    pub static ref REG: Registry = {
+        let mut reg = Default::default();
+        add_default_services(&mut reg);
+        reg
+    };
+}
+
+/// Register the builtin services of tvix_castore and tvix_store with the given
+/// registry. This is useful for creating your own registry with the builtin
+/// types _and_ extra third party types.
+pub fn add_default_services(reg: &mut Registry) {
+    tvix_castore::composition::add_default_services(reg);
+    crate::pathinfoservice::register_pathinfo_services(reg);
+}

tvix/store/src/lib.rs

@@ -1,3 +1,4 @@
+pub mod composition;
 pub mod import;
 pub mod nar;
 pub mod pathinfoservice;

tvix/store/src/pathinfoservice/bigtable.rs

@@ -10,15 +10,17 @@ use nix_compat::nixbase32;
 use prost::Message;
 use serde::{Deserialize, Serialize};
 use serde_with::{serde_as, DurationSeconds};
+use std::sync::Arc;
 use tonic::async_trait;
 use tracing::{instrument, trace};
+use tvix_castore::composition::{CompositionContext, ServiceBuilder};
 use tvix_castore::Error;
 
 /// There should not be more than 10 MiB in a single cell.
 /// https://cloud.google.com/bigtable/docs/schema-design#cells
 const CELL_SIZE_LIMIT: u64 = 10 * 1024 * 1024;
 
-/// Provides a [DirectoryService] implementation using
+/// Provides a [PathInfoService] implementation using
 /// [Bigtable](https://cloud.google.com/bigtable/docs/)
 /// as an underlying K/V store.
 ///
@@ -44,57 +46,6 @@ pub struct BigtablePathInfoService {
     emulator: std::sync::Arc<(tempfile::TempDir, async_process::Child)>,
 }
 
-/// Represents configuration of [BigtablePathInfoService].
-/// This currently conflates both connect parameters and data model/client
-/// behaviour parameters.
-#[serde_as]
-#[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
-pub struct BigtableParameters {
-    project_id: String,
-    instance_name: String,
-    #[serde(default)]
-    is_read_only: bool,
-    #[serde(default = "default_channel_size")]
-    channel_size: usize,
-
-    #[serde_as(as = "Option<DurationSeconds<String>>")]
-    #[serde(default = "default_timeout")]
-    timeout: Option<std::time::Duration>,
-    table_name: String,
-    family_name: String,
-
-    #[serde(default = "default_app_profile_id")]
-    app_profile_id: String,
-}
-
-impl BigtableParameters {
-    #[cfg(test)]
-    pub fn default_for_tests() -> Self {
-        Self {
-            project_id: "project-1".into(),
-            instance_name: "instance-1".into(),
-            is_read_only: false,
-            channel_size: default_channel_size(),
-            timeout: default_timeout(),
-            table_name: "table-1".into(),
-            family_name: "cf1".into(),
-            app_profile_id: default_app_profile_id(),
-        }
-    }
-}
-
-fn default_app_profile_id() -> String {
-    "default".to_owned()
-}
-
-fn default_channel_size() -> usize {
-    4
-}
-
-fn default_timeout() -> Option<std::time::Duration> {
-    Some(std::time::Duration::from_secs(4))
-}
-
 impl BigtablePathInfoService {
     #[cfg(not(test))]
     pub async fn connect(params: BigtableParameters) -> Result<Self, bigtable::Error> {
@@ -412,3 +363,88 @@ impl PathInfoService for BigtablePathInfoService {
         Box::pin(stream)
     }
 }
+
+/// Represents configuration of [BigtablePathInfoService].
+/// This currently conflates both connect parameters and data model/client
+/// behaviour parameters.
+#[serde_as]
+#[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
+pub struct BigtableParameters {
+    project_id: String,
+    instance_name: String,
+    #[serde(default)]
+    is_read_only: bool,
+    #[serde(default = "default_channel_size")]
+    channel_size: usize,
+
+    #[serde_as(as = "Option<DurationSeconds<String>>")]
+    #[serde(default = "default_timeout")]
+    timeout: Option<std::time::Duration>,
+    table_name: String,
+    family_name: String,
+
+    #[serde(default = "default_app_profile_id")]
+    app_profile_id: String,
+}
+
+impl BigtableParameters {
+    #[cfg(test)]
+    pub fn default_for_tests() -> Self {
+        Self {
+            project_id: "project-1".into(),
+            instance_name: "instance-1".into(),
+            is_read_only: false,
+            channel_size: default_channel_size(),
+            timeout: default_timeout(),
+            table_name: "table-1".into(),
+            family_name: "cf1".into(),
+            app_profile_id: default_app_profile_id(),
+        }
+    }
+}
+
+fn default_app_profile_id() -> String {
+    "default".to_owned()
+}
+
+fn default_channel_size() -> usize {
+    4
+}
+
+fn default_timeout() -> Option<std::time::Duration> {
+    Some(std::time::Duration::from_secs(4))
+}
+
+#[async_trait]
+impl ServiceBuilder for BigtableParameters {
+    type Output = dyn PathInfoService;
+    async fn build<'a>(
+        &'a self,
+        _instance_name: &str,
+        _context: &CompositionContext,
+    ) -> Result<Arc<dyn PathInfoService>, Box<dyn std::error::Error + Send + Sync>> {
+        Ok(Arc::new(
+            BigtablePathInfoService::connect(self.clone()).await?,
+        ))
+    }
+}
+
+impl TryFrom<url::Url> for BigtableParameters {
+    type Error = Box<dyn std::error::Error + Send + Sync>;
+    fn try_from(mut url: url::Url) -> Result<Self, Self::Error> {
+        // parse the instance name from the hostname.
+        let instance_name = url
+            .host_str()
+            .ok_or_else(|| Error::StorageError("instance name missing".into()))?
+            .to_string();
+
+        // … but add it to the query string now, so we just need to parse that.
+        url.query_pairs_mut()
+            .append_pair("instance_name", &instance_name);
+
+        let params: BigtableParameters = serde_qs::from_str(url.query().unwrap_or_default())
+            .map_err(|e| Error::InvalidRequest(format!("failed to parse parameters: {}", e)))?;
+
+        Ok(params)
+    }
+}

tvix/store/src/pathinfoservice/combinators.rs

@@ -1,8 +1,11 @@
+use std::sync::Arc;
+
 use crate::proto::PathInfo;
 use futures::stream::BoxStream;
 use nix_compat::nixbase32;
 use tonic::async_trait;
 use tracing::{debug, instrument};
+use tvix_castore::composition::{CompositionContext, ServiceBuilder};
 use tvix_castore::Error;
 
 use super::PathInfoService;
@@ -61,6 +64,41 @@ where
     }
 }
 
+#[derive(serde::Deserialize)]
+pub struct CacheConfig {
+    pub near: String,
+    pub far: String,
+}
+
+impl TryFrom<url::Url> for CacheConfig {
+    type Error = Box<dyn std::error::Error + Send + Sync>;
+    fn try_from(_url: url::Url) -> Result<Self, Self::Error> {
+        Err(Error::StorageError(
+            "Instantiating a CombinedPathInfoService from a url is not supported".into(),
+        )
+        .into())
+    }
+}
+
+#[async_trait]
+impl ServiceBuilder for CacheConfig {
+    type Output = dyn PathInfoService;
+    async fn build<'a>(
+        &'a self,
+        _instance_name: &str,
+        context: &CompositionContext,
+    ) -> Result<Arc<dyn PathInfoService>, Box<dyn std::error::Error + Send + Sync + 'static>> {
+        let (near, far) = futures::join!(
+            context.resolve(self.near.clone()),
+            context.resolve(self.far.clone())
+        );
+        Ok(Arc::new(Cache {
+            near: near?,
+            far: far?,
+        }))
+    }
+}
+
 #[cfg(test)]
 mod test {
     use std::num::NonZeroUsize;

tvix/store/src/pathinfoservice/from_addr.rs

@@ -1,13 +1,10 @@
-use crate::proto::path_info_service_client::PathInfoServiceClient;
+use super::PathInfoService;
 
-use super::{
-    GRPCPathInfoService, MemoryPathInfoService, NixHTTPPathInfoService, PathInfoService,
-    SledPathInfoService,
+use crate::composition::{
+    with_registry, CompositionContext, DeserializeWithRegistry, ServiceBuilder, REG,
 };
-
-use nix_compat::narinfo;
 use std::sync::Arc;
-use tvix_castore::{blobservice::BlobService, directoryservice::DirectoryService, Error};
+use tvix_castore::Error;
 use url::Url;
 
 /// Constructs a new instance of a [PathInfoService] from an URI.
@@ -34,113 +31,21 @@ use url::Url;
 /// these also need to be passed in.
 pub async fn from_addr(
     uri: &str,
-    blob_service: Arc<dyn BlobService>,
-    directory_service: Arc<dyn DirectoryService>,
-) -> Result<Box<dyn PathInfoService>, Error> {
+    context: Option<&CompositionContext<'_>>,
+) -> Result<Arc<dyn PathInfoService>, Box<dyn std::error::Error + Send + Sync>> {
     #[allow(unused_mut)]
     let mut url =
         Url::parse(uri).map_err(|e| Error::StorageError(format!("unable to parse url: {}", e)))?;
 
-    let path_info_service: Box<dyn PathInfoService> = match url.scheme() {
-        "memory" => {
-            // memory doesn't support host or path in the URL.
-            if url.has_host() || !url.path().is_empty() {
-                return Err(Error::StorageError("invalid url".to_string()));
-            }
-            Box::<MemoryPathInfoService>::default()
-        }
-        "sled" => {
-            // sled doesn't support host, and a path can be provided (otherwise
-            // it'll live in memory only).
-            if url.has_host() {
-                return Err(Error::StorageError("no host allowed".to_string()));
-            }
-
-            if url.path() == "/" {
-                return Err(Error::StorageError(
-                    "cowardly refusing to open / with sled".to_string(),
-                ));
-            }
-
-            // TODO: expose other parameters as URL parameters?
-
-            Box::new(if url.path().is_empty() {
-                SledPathInfoService::new_temporary()
-                    .map_err(|e| Error::StorageError(e.to_string()))?
-            } else {
-                SledPathInfoService::new(url.path())
-                    .map_err(|e| Error::StorageError(e.to_string()))?
-            })
-        }
-        "nix+http" | "nix+https" => {
-            // Stringify the URL and remove the nix+ prefix.
-            // We can't use `url.set_scheme(rest)`, as it disallows
-            // setting something http(s) that previously wasn't.
-            let new_url = Url::parse(url.to_string().strip_prefix("nix+").unwrap()).unwrap();
-
-            let mut nix_http_path_info_service =
-                NixHTTPPathInfoService::new(new_url, blob_service, directory_service);
-
-            let pairs = &url.query_pairs();
-            for (k, v) in pairs.into_iter() {
-                if k == "trusted-public-keys" {
-                    let pubkey_strs: Vec<_> = v.split_ascii_whitespace().collect();
-
-                    let mut pubkeys: Vec<narinfo::PubKey> = Vec::with_capacity(pubkey_strs.len());
-                    for pubkey_str in pubkey_strs {
-                        pubkeys.push(narinfo::PubKey::parse(pubkey_str).map_err(|e| {
-                            Error::StorageError(format!("invalid public key: {e}"))
-                        })?);
-                    }
-
-                    nix_http_path_info_service.set_public_keys(pubkeys);
-                }
-            }
-
-            Box::new(nix_http_path_info_service)
-        }
-        scheme if scheme.starts_with("grpc+") => {
-            // schemes starting with grpc+ go to the GRPCPathInfoService.
-            //   That's normally grpc+unix for unix sockets, and grpc+http(s) for the HTTP counterparts.
-            // - In the case of unix sockets, there must be a path, but may not be a host.
-            // - In the case of non-unix sockets, there must be a host, but no path.
-            // Constructing the channel is handled by tvix_castore::channel::from_url.
-            Box::new(GRPCPathInfoService::from_client(
-                PathInfoServiceClient::with_interceptor(
-                    tvix_castore::tonic::channel_from_url(&url).await?,
-                    tvix_tracing::propagate::tonic::send_trace,
-                ),
-            ))
-        }
-        #[cfg(feature = "cloud")]
-        "bigtable" => {
-            use super::bigtable::BigtableParameters;
-            use super::BigtablePathInfoService;
-
-            // parse the instance name from the hostname.
-            let instance_name = url
-                .host_str()
-                .ok_or_else(|| Error::StorageError("instance name missing".into()))?
-                .to_string();
-
-            // … but add it to the query string now, so we just need to parse that.
-            url.query_pairs_mut()
-                .append_pair("instance_name", &instance_name);
-
-            let params: BigtableParameters = serde_qs::from_str(url.query().unwrap_or_default())
-                .map_err(|e| Error::InvalidRequest(format!("failed to parse parameters: {}", e)))?;
-
-            Box::new(
-                BigtablePathInfoService::connect(params)
-                    .await
-                    .map_err(|e| Error::StorageError(e.to_string()))?,
-            )
-        }
-        _ => Err(Error::StorageError(format!(
-            "unknown scheme: {}",
-            url.scheme()
-        )))?,
-    };
+    let path_info_service_config = with_registry(&REG, || {
+        <DeserializeWithRegistry<Box<dyn ServiceBuilder<Output = dyn PathInfoService>>>>::try_from(
+            url,
+        )
+    })?
+    .0;
+    let path_info_service = path_info_service_config
+        .build("anonymous", context.unwrap_or(&CompositionContext::blank()))
+        .await?;
 
     Ok(path_info_service)
 }
@@ -148,14 +53,12 @@ pub async fn from_addr(
 #[cfg(test)]
 mod tests {
     use super::from_addr;
+    use crate::composition::{Composition, DeserializeWithRegistry, ServiceBuilder};
     use lazy_static::lazy_static;
     use rstest::rstest;
-    use std::sync::Arc;
     use tempfile::TempDir;
-    use tvix_castore::{
-        blobservice::{BlobService, MemoryBlobService},
-        directoryservice::{DirectoryService, MemoryDirectoryService},
-    };
+    use tvix_castore::blobservice::{BlobService, MemoryBlobServiceConfig};
+    use tvix_castore::directoryservice::{DirectoryService, MemoryDirectoryServiceConfig};
 
     lazy_static! {
         static ref TMPDIR_SLED_1: TempDir = TempDir::new().unwrap();
@@ -224,11 +127,19 @@ mod tests {
     )]
     #[tokio::test]
     async fn test_from_addr_tokio(#[case] uri_str: &str, #[case] exp_succeed: bool) {
-        let blob_service: Arc<dyn BlobService> = Arc::from(MemoryBlobService::default());
-        let directory_service: Arc<dyn DirectoryService> =
-            Arc::from(MemoryDirectoryService::default());
+        let mut comp = Composition::default();
+        comp.extend(vec![(
+            "default".into(),
+            DeserializeWithRegistry(Box::new(MemoryBlobServiceConfig {})
+                as Box<dyn ServiceBuilder<Output = dyn BlobService>>),
+        )]);
+        comp.extend(vec![(
+            "default".into(),
+            DeserializeWithRegistry(Box::new(MemoryDirectoryServiceConfig {})
+                as Box<dyn ServiceBuilder<Output = dyn DirectoryService>>),
+        )]);
 
-        let resp = from_addr(uri_str, blob_service, directory_service).await;
+        let resp = from_addr(uri_str, Some(&comp.context())).await;
 
         if exp_succeed {
             resp.expect("should succeed");

tvix/store/src/pathinfoservice/grpc.rs

@@ -6,9 +6,11 @@ use crate::{
 use async_stream::try_stream;
 use futures::stream::BoxStream;
 use nix_compat::nixbase32;
+use std::sync::Arc;
 use tonic::{async_trait, Code};
 use tracing::{instrument, Span};
 use tracing_indicatif::span_ext::IndicatifSpanExt;
+use tvix_castore::composition::{CompositionContext, ServiceBuilder};
 use tvix_castore::{proto as castorepb, Error};
 
 /// Connects to a (remote) tvix-store PathInfoService over gRPC.
@@ -149,6 +151,40 @@ where
     }
 }
 
+#[derive(serde::Deserialize, Debug)]
+#[serde(deny_unknown_fields)]
+pub struct GRPCPathInfoServiceConfig {
+    url: String,
+}
+
+impl TryFrom<url::Url> for GRPCPathInfoServiceConfig {
+    type Error = Box<dyn std::error::Error + Send + Sync>;
+    fn try_from(url: url::Url) -> Result<Self, Self::Error> {
+        //   normally grpc+unix for unix sockets, and grpc+http(s) for the HTTP counterparts.
+        // - In the case of unix sockets, there must be a path, but may not be a host.
+        // - In the case of non-unix sockets, there must be a host, but no path.
+        // Constructing the channel is handled by tvix_castore::channel::from_url.
+        Ok(GRPCPathInfoServiceConfig {
+            url: url.to_string(),
+        })
+    }
+}
+
+#[async_trait]
+impl ServiceBuilder for GRPCPathInfoServiceConfig {
+    type Output = dyn PathInfoService;
+    async fn build<'a>(
+        &'a self,
+        _instance_name: &str,
+        _context: &CompositionContext,
+    ) -> Result<Arc<dyn PathInfoService>, Box<dyn std::error::Error + Send + Sync + 'static>> {
+        let client = proto::path_info_service_client::PathInfoServiceClient::new(
+            tvix_castore::tonic::channel_from_url(&self.url.parse()?).await?,
+        );
+        Ok(Arc::new(GRPCPathInfoService::from_client(client)))
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::pathinfoservice::tests::make_grpc_path_info_service_client;

tvix/store/src/pathinfoservice/lru.rs

@@ -9,6 +9,7 @@ use tonic::async_trait;
 use tracing::instrument;
 
 use crate::proto::PathInfo;
+use tvix_castore::composition::{CompositionContext, ServiceBuilder};
 use tvix_castore::Error;
 
 use super::PathInfoService;
@@ -60,6 +61,34 @@ impl PathInfoService for LruPathInfoService {
     }
 }
 
+#[derive(serde::Deserialize, Debug)]
+#[serde(deny_unknown_fields)]
+pub struct LruPathInfoServiceConfig {
+    capacity: NonZeroUsize,
+}
+
+impl TryFrom<url::Url> for LruPathInfoServiceConfig {
+    type Error = Box<dyn std::error::Error + Send + Sync>;
+    fn try_from(_url: url::Url) -> Result<Self, Self::Error> {
+        Err(Error::StorageError(
+            "Instantiating a LruPathInfoService from a url is not supported".into(),
+        )
+        .into())
+    }
+}
+
+#[async_trait]
+impl ServiceBuilder for LruPathInfoServiceConfig {
+    type Output = dyn PathInfoService;
+    async fn build<'a>(
+        &'a self,
+        _instance_name: &str,
+        _context: &CompositionContext,
+    ) -> Result<Arc<dyn PathInfoService>, Box<dyn std::error::Error + Send + Sync + 'static>> {
+        Ok(Arc::new(LruPathInfoService::with_capacity(self.capacity)))
+    }
+}
+
 #[cfg(test)]
 mod test {
     use std::num::NonZeroUsize;

tvix/store/src/pathinfoservice/memory.rs

@@ -7,6 +7,7 @@ use std::{collections::HashMap, sync::Arc};
 use tokio::sync::RwLock;
 use tonic::async_trait;
 use tracing::instrument;
+use tvix_castore::composition::{CompositionContext, ServiceBuilder};
 use tvix_castore::Error;
 
 #[derive(Default)]
@@ -59,3 +60,30 @@ impl PathInfoService for MemoryPathInfoService {
         })
     }
 }
+
+#[derive(serde::Deserialize, Debug)]
+#[serde(deny_unknown_fields)]
+pub struct MemoryPathInfoServiceConfig {}
+
+impl TryFrom<url::Url> for MemoryPathInfoServiceConfig {
+    type Error = Box<dyn std::error::Error + Send + Sync>;
+    fn try_from(url: url::Url) -> Result<Self, Self::Error> {
+        // memory doesn't support host or path in the URL.
+        if url.has_host() || !url.path().is_empty() {
+            return Err(Error::StorageError("invalid url".to_string()).into());
+        }
+        Ok(MemoryPathInfoServiceConfig {})
+    }
+}
+
+#[async_trait]
+impl ServiceBuilder for MemoryPathInfoServiceConfig {
+    type Output = dyn PathInfoService;
+    async fn build<'a>(
+        &'a self,
+        _instance_name: &str,
+        _context: &CompositionContext,
+    ) -> Result<Arc<dyn PathInfoService>, Box<dyn std::error::Error + Send + Sync + 'static>> {
+        Ok(Arc::new(MemoryPathInfoService::default()))
+    }
+}

tvix/store/src/pathinfoservice/mod.rs

@@ -14,22 +14,26 @@ mod tests;
 
 use futures::stream::BoxStream;
 use tonic::async_trait;
+use tvix_castore::composition::{Registry, ServiceBuilder};
 use tvix_castore::Error;
 
+use crate::nar::NarCalculationService;
 use crate::proto::PathInfo;
 
-pub use self::combinators::Cache as CachePathInfoService;
+pub use self::combinators::{
+    Cache as CachePathInfoService, CacheConfig as CachePathInfoServiceConfig,
+};
 pub use self::from_addr::from_addr;
-pub use self::grpc::GRPCPathInfoService;
-pub use self::lru::LruPathInfoService;
-pub use self::memory::MemoryPathInfoService;
-pub use self::nix_http::NixHTTPPathInfoService;
-pub use self::sled::SledPathInfoService;
+pub use self::grpc::{GRPCPathInfoService, GRPCPathInfoServiceConfig};
+pub use self::lru::{LruPathInfoService, LruPathInfoServiceConfig};
+pub use self::memory::{MemoryPathInfoService, MemoryPathInfoServiceConfig};
+pub use self::nix_http::{NixHTTPPathInfoService, NixHTTPPathInfoServiceConfig};
+pub use self::sled::{SledPathInfoService, SledPathInfoServiceConfig};
 
 #[cfg(feature = "cloud")]
 mod bigtable;
 #[cfg(feature = "cloud")]
-pub use self::bigtable::BigtablePathInfoService;
+pub use self::bigtable::{BigtableParameters, BigtablePathInfoService};
 
 #[cfg(any(feature = "fuse", feature = "virtiofs"))]
 pub use self::fs::make_fs;
@@ -52,12 +56,16 @@ pub trait PathInfoService: Send + Sync {
     /// Rust doesn't support this as a generic in traits yet. This is the same thing that
     /// [async_trait] generates, but for streams instead of futures.
     fn list(&self) -> BoxStream<'static, Result<PathInfo, Error>>;
+
+    fn nar_calculation_service(&self) -> Option<Box<dyn NarCalculationService>> {
+        None
+    }
 }
 
 #[async_trait]
 impl<A> PathInfoService for A
 where
-    A: AsRef<dyn PathInfoService> + Send + Sync,
+    A: AsRef<dyn PathInfoService> + Send + Sync + 'static,
 {
     async fn get(&self, digest: [u8; 20]) -> Result<Option<PathInfo>, Error> {
         self.as_ref().get(digest).await
@@ -71,3 +79,19 @@ where
         self.as_ref().list()
     }
 }
+
+/// Registers the builtin PathInfoService implementations with the registry
+pub(crate) fn register_pathinfo_services(reg: &mut Registry) {
+    reg.register::<Box<dyn ServiceBuilder<Output = dyn PathInfoService>>, CachePathInfoServiceConfig>("cache");
+    reg.register::<Box<dyn ServiceBuilder<Output = dyn PathInfoService>>, GRPCPathInfoServiceConfig>("grpc");
+    reg.register::<Box<dyn ServiceBuilder<Output = dyn PathInfoService>>, LruPathInfoServiceConfig>("lru");
+    reg.register::<Box<dyn ServiceBuilder<Output = dyn PathInfoService>>, MemoryPathInfoServiceConfig>("memory");
+    reg.register::<Box<dyn ServiceBuilder<Output = dyn PathInfoService>>, NixHTTPPathInfoServiceConfig>("nix");
+    reg.register::<Box<dyn ServiceBuilder<Output = dyn PathInfoService>>, SledPathInfoServiceConfig>("sled");
+    #[cfg(feature = "cloud")]
+    {
+        reg.register::<Box<dyn ServiceBuilder<Output = dyn PathInfoService>>, BigtableParameters>(
+            "bigtable",
+        );
+    }
+}

tvix/store/src/pathinfoservice/nix_http.rs

@@ -7,12 +7,15 @@ use nix_compat::{
     nixhash::NixHash,
 };
 use reqwest::StatusCode;
+use std::sync::Arc;
 use tokio::io::{self, AsyncRead};
 use tonic::async_trait;
 use tracing::{debug, instrument, warn};
+use tvix_castore::composition::{CompositionContext, ServiceBuilder};
 use tvix_castore::{
     blobservice::BlobService, directoryservice::DirectoryService, proto as castorepb, Error,
 };
+use url::Url;
 
 /// NixHTTPPathInfoService acts as a bridge in between the Nix HTTP Binary cache
 /// protocol provided by Nix binary caches such as cache.nixos.org, and the Tvix
@@ -249,3 +252,71 @@ where
         }))
     }
 }
+
+#[derive(serde::Deserialize)]
+pub struct NixHTTPPathInfoServiceConfig {
+    base_url: String,
+    blob_service: String,
+    directory_service: String,
+    #[serde(default)]
+    /// An optional list of [narinfo::PubKey].
+    /// If set, the .narinfo files received need to have correct signature by at least one of these.
+    public_keys: Option<Vec<String>>,
+}
+
+impl TryFrom<Url> for NixHTTPPathInfoServiceConfig {
+    type Error = Box<dyn std::error::Error + Send + Sync>;
+    fn try_from(url: Url) -> Result<Self, Self::Error> {
+        let mut public_keys: Option<Vec<String>> = None;
+        for (_, v) in url
+            .query_pairs()
+            .into_iter()
+            .filter(|(k, _)| k == "trusted-public-keys")
+        {
+            public_keys
+                .get_or_insert(Default::default())
+                .extend(v.split_ascii_whitespace().map(ToString::to_string));
+        }
+        Ok(NixHTTPPathInfoServiceConfig {
+            // Stringify the URL and remove the nix+ prefix.
+            // We can't use `url.set_scheme(rest)`, as it disallows
+            // setting something http(s) that previously wasn't.
+            base_url: url.to_string().strip_prefix("nix+").unwrap().to_string(),
+            blob_service: "default".to_string(),
+            directory_service: "default".to_string(),
+            public_keys,
+        })
+    }
+}
+
+#[async_trait]
+impl ServiceBuilder for NixHTTPPathInfoServiceConfig {
+    type Output = dyn PathInfoService;
+    async fn build<'a>(
+        &'a self,
+        _instance_name: &str,
+        context: &CompositionContext,
+    ) -> Result<Arc<dyn PathInfoService>, Box<dyn std::error::Error + Send + Sync + 'static>> {
+        let (blob_service, directory_service) = futures::join!(
+            context.resolve(self.blob_service.clone()),
+            context.resolve(self.directory_service.clone())
+        );
+        let mut svc = NixHTTPPathInfoService::new(
+            Url::parse(&self.base_url)?,
+            blob_service?,
+            directory_service?,
+        );
+        if let Some(public_keys) = &self.public_keys {
+            svc.set_public_keys(
+                public_keys
+                    .iter()
+                    .map(|pubkey_str| {
+                        narinfo::PubKey::parse(pubkey_str)
+                            .map_err(|e| Error::StorageError(format!("invalid public key: {e}")))
+                    })
+                    .collect::<Result<Vec<_>, Error>>()?,
+            );
+        }
+        Ok(Arc::new(svc))
+    }
+}

tvix/store/src/pathinfoservice/sled.rs

@@ -5,8 +5,10 @@ use futures::stream::BoxStream;
 use nix_compat::nixbase32;
 use prost::Message;
 use std::path::Path;
+use std::sync::Arc;
 use tonic::async_trait;
 use tracing::{instrument, warn};
+use tvix_castore::composition::{CompositionContext, ServiceBuilder};
 use tvix_castore::Error;
 
 /// SledPathInfoService stores PathInfo in a [sled](https://github.com/spacejam/sled).
@@ -114,3 +116,69 @@ impl PathInfoService for SledPathInfoService {
         })
     }
 }
+
+#[derive(serde::Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct SledPathInfoServiceConfig {
+    is_temporary: bool,
+    #[serde(default)]
+    /// required when is_temporary = false
+    path: Option<String>,
+}
+
+impl TryFrom<url::Url> for SledPathInfoServiceConfig {
+    type Error = Box<dyn std::error::Error + Send + Sync>;
+    fn try_from(url: url::Url) -> Result<Self, Self::Error> {
+        // sled doesn't support host, and a path can be provided (otherwise
+        // it'll live in memory only).
+        if url.has_host() {
+            return Err(Error::StorageError("no host allowed".to_string()).into());
+        }
+
+        // TODO: expose compression and other parameters as URL parameters?
+
+        Ok(if url.path().is_empty() {
+            SledPathInfoServiceConfig {
+                is_temporary: true,
+                path: None,
+            }
+        } else {
+            SledPathInfoServiceConfig {
+                is_temporary: false,
+                path: Some(url.path().to_string()),
+            }
+        })
+    }
+}
+
+#[async_trait]
+impl ServiceBuilder for SledPathInfoServiceConfig {
+    type Output = dyn PathInfoService;
+    async fn build<'a>(
+        &'a self,
+        _instance_name: &str,
+        _context: &CompositionContext,
+    ) -> Result<Arc<dyn PathInfoService>, Box<dyn std::error::Error + Send + Sync + 'static>> {
+        match self {
+            SledPathInfoServiceConfig {
+                is_temporary: true,
+                path: None,
+            } => Ok(Arc::new(SledPathInfoService::new_temporary()?)),
+            SledPathInfoServiceConfig {
+                is_temporary: true,
+                path: Some(_),
+            } => Err(
+                Error::StorageError("Temporary SledPathInfoService can not have path".into())
+                    .into(),
+            ),
+            SledPathInfoServiceConfig {
+                is_temporary: false,
+                path: None,
+            } => Err(Error::StorageError("SledPathInfoService is missing path".into()).into()),
+            SledPathInfoServiceConfig {
+                is_temporary: false,
+                path: Some(path),
+            } => Ok(Arc::new(SledPathInfoService::new(path)?)),
+        }
+    }
+}

tvix/store/src/utils.rs

@@ -1,18 +1,60 @@
-use std::sync::Arc;
 use std::{
+    collections::HashMap,
     pin::Pin,
+    sync::Arc,
     task::{self, Poll},
 };
 use tokio::io::{self, AsyncWrite};
 
-use tvix_castore::{
-    blobservice::{self, BlobService},
-    directoryservice::{self, DirectoryService},
-};
+use tvix_castore::{blobservice::BlobService, directoryservice::DirectoryService};
 use url::Url;
 
+use crate::composition::{
+    with_registry, Composition, DeserializeWithRegistry, ServiceBuilder, REG,
+};
 use crate::nar::{NarCalculationService, SimpleRenderer};
-use crate::pathinfoservice::{self, PathInfoService};
+use crate::pathinfoservice::PathInfoService;
+
+#[derive(serde::Deserialize, Default)]
+pub struct CompositionConfigs {
+    pub blobservices:
+        HashMap<String, DeserializeWithRegistry<Box<dyn ServiceBuilder<Output = dyn BlobService>>>>,
+    pub directoryservices: HashMap<
+        String,
+        DeserializeWithRegistry<Box<dyn ServiceBuilder<Output = dyn DirectoryService>>>,
+    >,
+    pub pathinfoservices: HashMap<
+        String,
+        DeserializeWithRegistry<Box<dyn ServiceBuilder<Output = dyn PathInfoService>>>,
+    >,
+}
+
+pub fn addrs_to_configs(
+    blob_service_addr: impl AsRef<str>,
+    directory_service_addr: impl AsRef<str>,
+    path_info_service_addr: impl AsRef<str>,
+) -> Result<CompositionConfigs, Box<dyn std::error::Error + Send + Sync>> {
+    let mut configs: CompositionConfigs = Default::default();
+
+    let blob_service_url = Url::parse(blob_service_addr.as_ref())?;
+    let directory_service_url = Url::parse(directory_service_addr.as_ref())?;
+    let path_info_service_url = Url::parse(path_info_service_addr.as_ref())?;
+
+    configs.blobservices.insert(
+        "default".into(),
+        with_registry(&REG, || blob_service_url.try_into())?,
+    );
+    configs.directoryservices.insert(
+        "default".into(),
+        with_registry(&REG, || directory_service_url.try_into())?,
+    );
+    configs.pathinfoservices.insert(
+        "default".into(),
+        with_registry(&REG, || path_info_service_url.try_into())?,
+    );
+
+    Ok(configs)
+}
 
 /// Construct the store handles from their addrs.
 pub async fn construct_services(
@@ -23,49 +65,52 @@ pub async fn construct_services(
     (
         Arc<dyn BlobService>,
         Arc<dyn DirectoryService>,
-        Box<dyn PathInfoService>,
+        Arc<dyn PathInfoService>,
         Box<dyn NarCalculationService>,
     ),
     Box<dyn std::error::Error + Send + Sync>,
 > {
-    let blob_service: Arc<dyn BlobService> =
-        blobservice::from_addr(blob_service_addr.as_ref()).await?;
-    let directory_service: Arc<dyn DirectoryService> =
-        directoryservice::from_addr(directory_service_addr.as_ref()).await?;
+    let configs = addrs_to_configs(
+        blob_service_addr,
+        directory_service_addr,
+        path_info_service_addr,
+    )?;
+    construct_services_from_configs(configs).await
+}
 
-    let path_info_service = pathinfoservice::from_addr(
-        path_info_service_addr.as_ref(),
-        blob_service.clone(),
-        directory_service.clone(),
-    )
-    .await?;
+/// Construct the store handles from their addrs.
+pub async fn construct_services_from_configs(
+    configs: CompositionConfigs,
+) -> Result<
+    (
+        Arc<dyn BlobService>,
+        Arc<dyn DirectoryService>,
+        Arc<dyn PathInfoService>,
+        Box<dyn NarCalculationService>,
+    ),
+    Box<dyn std::error::Error + Send + Sync>,
+> {
+    let mut comp = Composition::default();
+
+    comp.extend(configs.blobservices);
+    comp.extend(configs.directoryservices);
+    comp.extend(configs.pathinfoservices);
+
+    let blob_service: Arc<dyn BlobService> = comp.build("default").await?;
+    let directory_service: Arc<dyn DirectoryService> = comp.build("default").await?;
+    let path_info_service: Arc<dyn PathInfoService> = comp.build("default").await?;
 
     // HACK: The grpc client also implements NarCalculationService, and we
     // really want to use it (otherwise we'd need to fetch everything again for hashing).
     // Until we revamped store composition and config, detect this special case here.
-    let nar_calculation_service: Box<dyn NarCalculationService> = {
-        use crate::pathinfoservice::GRPCPathInfoService;
-        use crate::proto::path_info_service_client::PathInfoServiceClient;
-
-        let url = Url::parse(path_info_service_addr.as_ref())
-            .map_err(|e| io::Error::other(e.to_string()))?;
-
-        if url.scheme().starts_with("grpc+") {
-            Box::new(GRPCPathInfoService::from_client(
-                PathInfoServiceClient::with_interceptor(
-                    tvix_castore::tonic::channel_from_url(&url)
-                        .await
-                        .map_err(|e| io::Error::other(e.to_string()))?,
-                    tvix_tracing::propagate::tonic::send_trace,
-                ),
-            ))
-        } else {
+    let nar_calculation_service: Box<dyn NarCalculationService> = path_info_service
+        .nar_calculation_service()
+        .unwrap_or_else(|| {
             Box::new(SimpleRenderer::new(
                 blob_service.clone(),
                 directory_service.clone(),
-            )) as Box<dyn NarCalculationService>
-        }
-    };
+            ))
+        });
 
     Ok((
         blob_service,